A Dry Sorbent Injection system directly injects a fine powder of dry sorbent into the duct downstream the combustion chamber. The alkaline sorbent reacts with acids in the flue gas and the dry reaction products are removed in the particulate collector or in the wet scrubber liquor. DSI technology was originally developed in the late '80s to respond to the EPA regulations on emission control of acid gasses for older power plants that required low cost easy retrofitting solutions. The alternative technologies are wet scrubbers, dry scrubbers and furnace sorbent injection.

Dry sorbent injection of hydrated lime is an effective approach for acid gas control, primarily due to its simplicity in process configurations, low capital costs, and in contrast to the sodium-based sorbents, the absence of ash handling concerns. Bag filters have been favored because the deposited dust layers contain unreactive sorbent that further reduces the acid gas content in the exhaust gases. DSI on ESP systems have been proven effective, especially with SO3 mitigation.